Aluminum alloy sheet for lithographic printing plate

ABSTRACT

The present invention provides an aluminum alloy sheet for a lithographic printing plate which allows pits to be uniformly formed by electrochemical roughening, and excels in strength and heat softening resistance. The aluminum alloy sheet for a lithographic printing plate includes 0.1-0.3% of Mg, more than 0.05%, but 0.5% or less of Zn, 0.2-0.6% of Fe, 0.03-0.15% of Si, 0.02% or less of Cu, and 0.003-0.05% of Ti, the remainder being Al and impurities. The aluminum alloy sheet may include more than 0.05%, but 0.3% or less of Mn.

BACKGROUND OF TED INVENTION

1. Field of the Invention

The present invention relates to an aluminum alloy sheet for a lithographic printing plate. More particularly, the present invention relates to an aluminum alloy sheet for a lithographic printing plate which con be uniformly roughened on the surface by electrochemical etching and exhibits excellent strength and heat softening resistance.

2. Description of Background Art

An aluminum alloy sheet is generally used as a support for a lithographic printing plate (including offset printing plate) A support is roughened on the surface from the viewpoint of improving adhesion to a photosensitive film and water retention properties in a non-image area.

As the surface roughening method, a mechanical roughening method ouch as ball graining, brush graining, or wire graining has been conventionally used. As the support, a JIS A1100 alloy (aluminum purity: 99.0%), a JIS A3003 alloy (aluminum purity: 98.0-98.5%), or the like has been used.

In recent years, a method of roughening the surface of the aluminum alloy sheet used as a support by electrochemical etching has rapidly developed, since this method ensures excellent processability and printing performance and enables continuous processing of a coiled material. In electrochemical etching, hydrochloric acid or an electrolyte containing hydrochloric acid as a major component (hereinafter called “hydrochloric acid electrolyte”), or nitric acid or an electrolyte containing nitric acid as a major component (herainafter called “nitric acid electrolyte”) is used as the electrolyte A JIS A1050 equivalent material (aluminum purity: 99.5%) which allows comparatively uniform electrolytic roughening is applied as the support. As many as one hundred thousand sheets of good impression can be obtained by appropriately selecting a photosensitive resin layer applied to the support.

In order to improve plate wear of the printing plate, a printing plate having an aluminum alloy sheet as the support is exposed and developed by using a conventional method, and an image area is strengthened by a high-temperature heat treatment (hereinafter called “burning treatment”). Since the burning treatment is usually performed at a beating temperature of 200-290° C. and a heating time of 3-9 minutes, the support must have heat resistance (burning resistance) to such an extent that the strength of the support does not decrease during the burning treatment.

In recent years, the printing speed has been increased accompanying improvement of printing technology. Therefore, stress applied to the printing plate mechanically secured to both sides of a printing cylinder of a printing machine is increased. Therefore, an increase in the strength of the support has been demanded. If the strength of the support is insufficient, the secured area is deformed or breaks, whereby a problem such as incorrect printing occurs. This makes it indispensable to improve the strength of the support in addition to the burning resistance.

In order to deal with such a demand, use of a support in which Mg or Zn is added to a JIS A1050 equivalent material has been attempted. As the support to which Mg is added, an aluminum alloy support containing 0.30-0.40% of Fe, 0.05-0.25% of Si, 0.04% or less of Cu, 0.05% or less of Mn, and 0.10-0.30% of Mg (see Japanese Patent Application Laid-open No. 2001-49313), an aluminum alloy support containing 0.05-0.3% of Mg, 0.03-0.3% of Si, 0.1-0.4% of Fe, and 0.05% or less of Cu (see Japanese Patent Application Laid-open NO. 61-146598), an aluminum alloy support containing 0.05-0.5% of Fe, 0.1-0.9% of Mg, 0.01-0.3% of at least one of V and Ni, 0.2% or less of Si, and 0.05% or less of Cu (see Japanese Patent Application Laid-open No. 62-230946), an aluminum alloy support containing 0.005-0.2% of Ng, 0.3% or less of Cu, and at least one of 1.5% or lass of Ma, 0.3% or less of Cr, 1.0% pr less of Fe, and 1.0% or leas of Si (see Japanese Patent Application Laid-open No. 59-93850), an aluminum alloy support containing 0.05-0.7% of Si, 0.05-3% of Mg, and 0.01-0.25% of Zr (see Japanese Patent Application Laid-open No. 62-74693), and the like have been proposed.

As the support to which Zn is added, an aluminum alloy support containing 0.25-0.6% of Fe, 0.03-0.1% of Si, 0.05% or Less of Cu, 0.05% or less of Ti, and 0.01-0.10% of En, and satisfying (Za %/2)+Ti %−Cu %≧0.003% (see Japanese Patent Application Laid-open No. 8-311592), an aluminum alloy support containing 0.20-0.6% of Fe, 0.03-0.1% of Si, and 0.04-0.1% of Zn, and satisfying Zn %/Fe %≧0.2% (see Japanese patent Application Laid-open No. 9-316582), an aluminum alloy support containing 0.11-0.60% of Fe, 0.01-0.20% of Si, 0.005-0.075% of Ni, 0.005-0.075% of Zn, and lees than 0.05% of Cu, and satisfying Zn %≦0.08−Ni % and Fe %≧0.1+Si % (see Japanese Patent Application Laid-open No. 2001-219662), a support for a lithographic printing plate made of an aluminum alloy containing 0.05-0.5% of Fe, 0.02-0.2% of Si, 0.001-0.05% of Zn, 0.003-0.04% of Ti, 0.001-0.3% of Mg, 0.001-0.05% of Mn, and 0.001-0.05% of Zu (see Japanese Patent Application Laid-open No. 2002-363799), and the, like have been proposed.

SUMMARY OF THE INVENTION

However, the above aluminum alloy sheet used as a support cannot entirely satisfy demands for uniform formation of pita by electrolytic roughening using the hydrochloric acid electrolyte or nitric acid electrolyte, high strength, and burning resistance, and does not necessarily have sufficient characteristics to deal with strong demands for adhesion to the photosensitive film, water retention properties in the non-image area, and the like.

In order to obtain an aluminum alloy sheet used as a support for a printing plate which can deal with strong demands for adhesion to the photosensitive film and water retention properties in the non-image area, further increase uniformity of pits formed by surface roughening, and satisfy demands for high strength and burning resistance, the present inventors have conducted further diversified studies on relevance of the content of components and the relationship among the components of the aluminum alloy support based on a JIS A1050 equivalent material with the above-described properties. As a result, the present inventors have found that the strength and heat resistance can be improved and excellent roughening properties can be obtained by adding Mg and Zn in specific amounts.

The present invention has been achieved based on the above findings. An object of the present invention is to provide an aluminum alloy sheet for a lithographic printing plate which allows formation of extremely uniform pits on the surface by electrochemical roughening to ensure further excellent adhesion to the photosensitive film and water retention properties, and excels in strength and burning resistance.

In order to achieve the above object, the present invention provides an aluminum alloy sheet for a lithographic printing plate, comprising 0.1-0.3% (mass %; hereinafter the same) of Mg, more than 0.05%, but 0.5% or less of Zn, 0.2-0,6% of Fe, 0.03-0.15% of Si, 0.02% or less of Cu, and 0.003-0.05% of Ti, the remainder being Al and impurities.

The present invention also provides an aluminum alloy sheet for a lithographic printing plate, comprising 0.1-0.3% of Ng, more than 0.05%, but 0.5% or less of Zn, more than 0.05, but 0.3% or less of Mn, 0.2-0.6% of Fe, 0.03-0.15% of Si, 0.03% or less of Cu, and 0.003-0.05% of Ti, the remainder being Al and impurities.

In the aluminum alloy sheet according to the present invention, the Mg content and the Zn content preferably satisfy a relationship expressed by 0.4×Zn %≦Mg %≦4×Zn %.

According to the present invention, an aluminum alloy sheet for a lithographic printing plate which allows pits to be uniformly formed by electrochemical roughening, exhibits excellent adhesion to a photosensitive film and water retention properties, achieves improved image clearness and plate wear, and excels in strength and heat softening resistance can be provided.

Other objects, features, and advantages of the invention will hereinafter become more readily apparent from the following description.

DETAILED DESCRIPTION OF THE INVENTION AND PREFERRED EMBODIMENT

Effects and reasons for limitations of the components of the aluminum alloy sheet for a lithographic printing plate of the present invention are described below.

Most of the Mg tends to present in aluminum alloy in dissolved condition and improves strength and heat softening resistance. The strength used herein refers to tensile strength as a support for a printing plate at room temperature., and is preferably 160 MPa or more in practical application. The heat softening resistance is also called burning resistance, and refers to 0.2% yield strength after heating at a temperature of about 280° C. The thermal softening resistance is preferably 90 MPa or more in practical application. The mg content is preferably 0.1-0.3%. If the Mg content is less than 0.1%, the effect is insufficient. If the Mg content exceeds 0.3%, uniformity of pits formed by surface roughening is decreased, whereby the non-image area tends to be stained.

Most of the Zn tends to present in aluminum alloy in dissolved condition in the same manner as Mg. However, Zn does not improve strength and heat softening resistance, differing from Mg, but affects an oxide film formed on the surface of aluminum. The oxide film formed on the surface of aluminum is divided into an oxide film formed when allowed to stand at room temperature (natural oxide film) and an oxide film formed during a heat treatment in the manufacturing process. Zn affects both of these oxide films.

Specifically, an oxide film containing an mg oxide (MgO oxide) as a major component is easily formed in an aluminum alloy containing Mg by a heat treatment for homogenization, hot rolling, or process annealing. Since this oxide film is active and porous, wettability with a treatment solution is improved during electrolytic roughening, whereby surface roughening is promoted. On the other hand, pits tend to become nonuniform. The addition of Zn reduces nonuniformity of the roughened structure and prevents activation due to the Mg oxide. The Zn content is preferably more than 0.05%, but 0.5% or less. If the Zn content is 0.05% or less, the effect is insufficient. If the Zn content exceeds 0.5%, since the retardation effect on activation due to the Mg oxide is increased, surface roughening becomes nonuniform. Moreover, since a coarse intermetallic compound is easily formed, a coarse pit is formed during electrolysis, whereby surface roughening becomes nonuniform to a greater extent. The Zn content is still more preferably 0.06-0.5%.

The Mg content and the Zn content preferably satisfy a relationship expressed by 0.4×Zn %≦Mg %≦4×Zn %. If 0.4×Zn %>Mg %, since the amount of Zn is in excess of the amount of Mg, the retardation affect on activation due to the Mg oxide is increased, whereby pits are nonuniformly formed during electrolysis. As a result, the roughened surface tends to become nonuniform. If Mg>4×Zn %, since the amount of Zu is insufficient for the amount of Mg, the retardation effect on activation due to the Mg oxide is small. In this case, pits are nonuniformly formed during electrolysis, whereby the roughened surface tends to become nonuniform.

Fe forms an Al—Fe intermetallic compound, and forms an Al—Fe—Si intermetallic compound with Si. These compounds are dispersed to refine the recrystalliation structure. These compounds act as starting points for formation of pits, whereby pits are uniformly and finely distributed during electrolysis. The Fe content is preferably 0.2-0.6%. If the Fe content is less than 0.2%, the distribution of the compounds becomes nonuniform, whereby pits are nonuniformly formed during electrolysis. If the Fe content exceeds 0.6, a coarse compound is formed, whereby uniformity of the roughened structure is decreased.

Si forms an Al—Fe—Si intermetallic compound with Fe. These compounds are dispersed to refine the recrystallization structure. These compounds act as starting points for formation of pits, whereby pits are uniformly and finely distributed during electrolysis. The Si content is preferably 0.03-0.15%. If the Si content is less than 0.03%, the distribution of the compounds becomes nonuniform, whereby pits are nonuniformly formed during electrolysis. If the Si content exceeds 0.15%, a coarse compound is formed. Moreover, precipitation of a single element Si tends to occur, whereby uniformity of the roughened structure is decreased.

Cu is easily dissolved in aluminum and is effective for

Obtaining fine pits when added in an amount of 0.03% or less (excluding 0%). If the Cu content exceeds 0.03%, pits tend to become coarse and nonuniform during electrolysis. In the present invention, the amount of Cu mixed from a ground metal employed to obtain the above described Fe and Si content is about 5-100 ppm (0.0005-0.01%).

Ti is effective for obtaining fine cast structure and for obtaining the crystal grains. As a result, Ti causes pits to be uniformly formed during electrolysis, thereby preventing occurrence of streaks when performing a treatment for a printing plate. The Ti Content is preferably 0.003-0.05%. If the Ti content is less than 0.003%, the effect is insufficient. If the Ti content exceeds 0.05%, a coarse Al—Ti compound is formed, whereby the roughened structure tends to become nonuniform. In the case of adding B together with Ti in order to refine the ingot structure, Ti is preferably added in an amount of 0.01% or less.

Mn improves strength and heat softening resistance. The Mn content is preferably more than 0.05%, but 0.3% or less. If the Mn content is 0.05% or less, the effect is insufficient. If the Mn content exceeds 0.3%, a coarse Al—Fe—Nn or Al—Fe—Mn—Si intermettalic compound is easily formed, whereby surface roughening tends to become nonuniform during electrolysis. The Mu content is still more preferably 0.06-0.3%.

The effect of the present invention is not impaired if the aluminum alloy sheet of the present invention contains 100 ppm or less of Pb, 100 ppm or less of Cr, 50 ppm or less of In, 50 ppm or less of Su, 50 ppm or less of Ni, 300 ppm or less of Ga, and 200 ppm or less of V.

The aluminum alloy sheet used as a support for a lithographic printing plate according to the present invention is manufactured by homogenizing an ingot of the above aluminum alloy, hot-rolling the homogenized product, and cold-rolling the hot-rolled product. Process annealing may be performed in the middle of cold rolling. For example, the ingot is homogenized at a temperature of 400-600° C., hot-rolled at a temperature of 350-600° C., and cold-rolled at a reduction ratio of 50-98%. In the case of performing process annealing, process annealing is performed after hot rolling under conditions where the hot-rolled product is maintained at 350-550° C. for 0-30 seconds in a continuous annealing furnace, and the annealed product is cold-rolled at a reduction ratio of 50-98%. Or, cold rolling is performed after hot rolling, process annealing is performed between the cold rolling, and final cold rolling is then performed,

EXAMPLES

The present invention is described below by comparing an example of the present invention with a comparative example. The effects of the present invention are remonstrated based on the comparison. The following example illustrates only one preferred embodiment of the present invention. The present invention is not limited to the following example.

Example 1

An aluminum alloy having a composition shown in Table 1 was dissolved and cast. The resulting ingot was machined on each side to a thickness of 500 mm, a width of 1000 mm, and a length of 3500 mm. The resulting product was homogenized at a temperature of 450° C., and hot-rolled at a temperature of 400° C. The hot-rolled product was cold-rolled and subjected to final cold rolling to obtain a sheet material with a thickness of 0.30 mm.

The tensile strength of the resulting aluminum alloy sheet was measured by performing a tensile test at room temperature. As an index of beat softening resistance, 0.2% yield strength was measured by performing a tensile test after heating the aluminum sheet for eight minutes in a burning processor maintained at a temperature of 280° C. The strength and burning resistance as a support were evaluated in this manner. The yield strength was measured in the direction (direction L) parallel to the rolling direction of the aluminum alloy sheet. The tensile strength at room temperature was evaluated as “Good” at 160 mPa or more, and evaluated as “Bad” at less than 160 MPa. The 0.2% yield strength after heating at 280° C. for eight minutes (hereinafter called “0.2% yield strength after heating”) was evaluated as “Good” at 90 MPa or more, and evaluated as “Bad” at leas than 90 MPa.

The resulting aluminum alloy sheet was degreased, washed with a neutralizer, and subjected to alternating current (AC) electrolytic roughening under conditions shown in Table 2. The resulting product was desmutted to remove an oxide formed by electrolysis, and then anodized. The resulting product was washed with water, dried, and out to a specific size to obtain a specimen.

The surface of each specimen was observed using a scanning electron microscope (SEM) at a magnification of 500, and photographed so that the area of the field of view was 0.04 mm². The specimen was evaluated as described below from the resulting photograph. The evaluation results are shown in Table 3. Occurrence of unetched area:

A specimen in which an unetched area accounted for more than 20% was evaluated as “Bad”, a specimen in which an unetched area accounted for 15-20% was evaluated as “Good”, and a specimen in which an unetched area accounted for less than 15% was evaluated as “Excellent”.

Etch Pit Uniformity:

A specimen in which large pits with a circle equivalent diameter exceeding 10 μm accounted for more than 20% of the entire pits in area ratio was evaluated as “Bad”, a specimen in which the area ratio was 10-20% was evaluated as “Good”, and a specimen in which the area ratio was less than 10% was evaluated as “Excellent”. TABLE 1 Composition (mass %) Relational equation between Alloy Mg Zn Mn Fe Si Cu Ti Mg and Zn A 0.25 0.06 0.002 0.30 0.06 0.003 0.015 Not satisfied B 0.20 0.11 0.002 0.30 0.06 0.003 0.015 Satisfied C 0.20 0.11 0.100 0.30 0.06 0.003 0.015 Satisfied D 0.20 0.11 0.300 0.30 0.06 0.003 0.015 Satisfied E 0.20 0.30 0.100 0.30 0.06 0.003 0.015 Satisfied F 0.20 0.48 0.300 0.30 0.06 0.003 0.015 Satisfied G 0.10 0.15 0.070 0.47 0.13 0.012 0.006 Satisfied H 0.29 0.24 0.290 0.22 0.04 0.028 0.031 Satisfied I 0.15 0.47 0.150 0.35 0.10 0.001 0.048 Not satisfied J 0.20 0.10 0.002 0.30 0.06 0.003 0.005 Satisfied <Note> Relational equation between Mg content and Zn content: Mg % > 4 × Zn % in Alloy A, and 0.4 × Zn % > Mg % in Alloy I.

TABLE 2 Treatment Treatment condition Degreasing Solution: 5% sodium hydroxide Temperature: 60° C. Duration: 10 seconds Neutralization Solution: 10% nitric acid Temperature: 20° C. Duration: 30 seconds AC electrolytic Solution: 2.0% hydrochloric acid roughening Temperature: 25° C. Frequency: 50 Hz Current density: 60 A/dm² Duration: 20 seconds Desmutting Solution: 5% sodium hydroxide Temperature: 60° C. Duration: 5 seconds Anodization Solution: 30% sulfuric acid Temperature: 20° C. Duration: 60 seconds

TABLE 3 Room temperature After heating Tensile Tensile Roughening properties strength strength Occurrence of Etch pit Specimen Alloy (MPa) Evaluation (MPa) Evaluation unetched area uniformity 1 A 165 Good 112 Good Good Good 2 B 168 Good 111 Good Excellent Excellent 3 C 177 Good 119 Good Excellent Good 4 D 185 Good 127 Good Excellent Good 5 E 278 Good 123 Good Excellent Excellent 6 F 190 Good 128 Good Good Excellent 7 G 170 Good 112 Good Good Excellent 8 H 190 Good 134 Good Good Excellent 9 I 175 Good 120 Good Good Good 10 J 180 Good 120 Good Excellent Excellent

As shown in Table 3, the specimens Nos. 1-10 according to the present invention excelled in support strength (tensile strength at room temperature) and burning resistance (0.2% yield strength after heating), and exhibited excellent roughening properties.

Comparative Example 1

An aluminum alloy having a composition shown in Table 4 was dissolved and cast. The resulting product was formed into a sheet material with a thickness of 0.30 mm according to the same steps as in Example 1. The resulting aluminum alloy sheet was subjected to measurements for 0.2% yield strength at room temperature and 0.2% yield strength after heating at 280° C. for eight minutes in the same manner as in Example 1. The aluminum alloy sheet was degreased, washed with a neutralizer, and subjected to AC electrolytic roughening under conditions shown in Table 2. The resulting product was desmutted to remove an oxide formed by electrolysis, and then anodised. The resulting product was washed with water, dried, and cut to a specific size to obtain a specimen. In Table 4, values outside the conditions of the present invention are underlined.

The surface of each specimen was observed using a scanning electron microscope (SEM) at a magnification of 500, and photographed so that the area of the field of view was 0.04 mm². Occurrence of an unetched area and etch pit uniformity were evaluated from the resulting photograph by using the same methods as in Example 1. The results are shown in Table 5. TABLE 4 Composition (mass %) Alloy Mg Zn Mn Fe Si Cu Ti K 0.05 0.10 0.10 0.30 0.06 0.003 0.015 L 0.50 0.10 0.10 0.30 0.06 0.003 0.015 M 0.20 0.02 0.002 0.30 0.06 0.003 0.015 N 0.20 0.70 0.10 0.30 0.06 0.003 0.015 O 0.20 0.10 0.50 0.30 0.06 0.003 0.015 P 0.20 0.10 0.10 0.12 0.06 0.003 0.015 Q 0.20 0.10 0.10 0.75 0.06 0.003 0.015 R 0.20 0.10 0.10 0.30 0.02 0.003 0.015 S 0.20 0.10 0.10 0.30 0.21 0.003 0.015 T 0.20 0.10 0.10 0.30 0.06 0.050 0.015 U 0.20 0.10 0.10 0.30 0.06 0.003 0.065 V 0.003 0.003 0.002 0.30 0.06 0.010 0.029

TABLE 5 Room temperature After heating Tensile Tensile Roughening properties strength strength Occurrence of Etch pit Specimen Alloy (MPa) Evaluation (Mpa) Evaluation unetched area uniformity 11 K 157 Bad 85 Bad Bad Bad 12 L 195 Good 130 Good Bad Bad 13 M 166 Good 111 Good Bad Bad 14 N 182 Good 120 Good Bad Bad 15 O 194 Good 131 Good Good Bad 16 P 175 Good 112 Good Good Bad 17 Q 190 Good 130 Good Bad Bad 18 R 178 Good 115 Good Good Bad 19 S 184 Good 123 Good Bad Bad 20 T 174 Good 122 Good Bad Bad 21 U 181 Good 115 Good Bad Bad 22 V 155 Bad 87 Bad Bad Bad

As shown in Table 5, the specimen No. 11 exhibited low tensile strength at room temperature and low 0.2% yield strength after heating due to low mg content. Moreover, the number of unetched areas was increased, and the pit were nonuniform. The specimen No. 12 showed variation in the size of pits due to high mg content. The size of pits was nonuniform in the specimen No. 13 due to low Zn content. A coarse pit was formed in the specimen No. 14 due to high Zn content. Moreover, the number of unetched areas was increased. A coarse pit was formed in the specimen No. 15 due to high Mn content, whereby the size of pits became nonuniform.

Pits were nonuniformly formed in the specimen No. 16 due to low Fe content. A coarse pit was formed and an unetched area occurred in the specimen No. 17 due to high Fe content. The specimen No. 18 showed variation in the size of pits due to low Si content. A coarse pit was formed in the specimen No. 19 due to high Si content, whereby the size of pits became nonuniform. The number of unetched areas was increased in the specimen No. 20 due to high Cu content.

A coarse pit was formed in the specimen No. 21 due to high Ti content. The specimen No. 22 exhibited low tensile strength at room temperature and low 0.2% yield strength after heating due to low Zn content and low Mn content.

Obviously, numerous modifications and variations of the present invention are possible in light of the above teachings. It is therefore to be understood that, within the scope of the appended claims, the invention may be practiced otherwise than as specifically described herein. 

1. An aluminum alloy sheet for a lithographic printing plate, comprising 0.1-0.3% of Mg, more than 0.05%, but 0.5% or less of Zn, 0.2-0.6% of Fe, 0.03-0.15% of Si, 0.02% or less (excluding 0%; hereinafter the same) of Cu, and 0.003-0.05% of Ti, the remainder being Al and impurities.
 2. An aluminum alloy sheet for a lithographic printing plate, comprising 0.1-0.3% of Mg, more than 0.05%, but 0.5% or less of Zn, more than 0.05, but 0.3% or less of Mn, 0.2-0.6% of Fe, 0.03-0.15% of Si, 0.02% or less of Cu, and 0.003-0.05% of Ti, the remainder being Al and impurities.
 3. The aluminum alloy sheet for a lithographic printing plate according to claim 1 or 2, wherein the Mg content and the Zn content satisfy a relationship expressed by 0.4×Zn %≦Mg %≦4×Zn %. 